Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$74.58	5.314%	$78.5432	$78.54	$78.55	$78.50
Purchase #2	$96.82	9.816%	$106.3239	$106.32	$106.30	$106.30
Purchase #3	$85.41	4.496%	$89.25	$89.25	$89.25	$89.30
Purchase #4	$137.63	12.670%	$155.0677	$155.07	$155.05	$155.10
Purchase #5	$151.39	9.501%	$165.7736	$165.77	$165.75	$165.80
Purchase #6	$45.52	7.116%	$48.7592	$48.76	$48.75	$48.80
Purchase #7	$38.28	9.343%	$41.8565	$41.86	$41.85	$41.90
7 purchase totals =	$629.63		$685.5741	$685.57	$685.50	$685.70